1. Field of the Invention
This invention relates to hydrological pulleys used in monitoring wells, and in particular to a lightning resistant hydrological pulley.
2. Background of the Invention
Monitoring wells are used extensively to observe and record subterranean water level. For example, in the state of Florida alone there are thousands of monitoring wells all across the state.
This measurement function is important, because the resultant data may be used to determine the amount of extra irrigation required by crops, to forecast rainfall trends, to help plan what specific types of crops to plant, as well as to aid in designing storm-water handling systems and flood control, etc.
A typical monitoring well 2 is illustrated in FIG. 1. Well shaft 4 extends below ground level 3 to a depth sufficient to reach water 5. Tape 8 depends from hydrological pulley 9, which is free to rotate as indicated by arrow 16. First weight 10 is attached to one extreme of tape 8; float 12 and second weight 14 are attached to an opposite extreme of tape 8.
As the water level 7 goes up and down, so also float 12 ascends and descends, thereby turning hydrological pulley 9 as indicated by arrow 16. Tape 8 is maintained taut over hydrological pulley 9 by means of first weight 10 and second weight 12. In practice, hydrological pulley 9 frequently comprises spikes 28 disposed within tape groove 26, which mate with spike holes 30 in tape 8. See also FIG. 2. Spikes 28 within spike holes 30 prevent tape 8 from slipping on hydrological pulley 9.
Hydrological pulley 9 is attached to encoder disk 20 by means of axle 18. Thus, as hydrological pulley 9 rotates, so also does encoder disk 20. Electronic sensor 22 senses rotation of encoder disk 20, and transmits this information to encoder 24. Encoder 24 collects data including direction and magnitude of rotation of encoder disk 20, which raw data yields a continuous record of the height of water level 7. A paper tape record may also be kept.
Because conventional tape 8 is made of stainless steel, and because conventional hydrological pulleys 9 are made of metal, a major problem associated with conventional monitoring wells 2 is the damage caused by lightning strikes to tape 8 and/or to hydrological pulley 9. Because stainless steel and metal conduct electricity, any lighting strike to tape 8 or hydrological pulley 9 will be conducted through axle 18, encoder disk 20 and electronic sensor 22 to encoder 24. The voltage of lightning strikes runs in the millions of volts, which generally has the effect of destroying the encoder 24 electronics and sensor 22, and may damage encoder disk 20. The replacement cost of these components runs between $400 and $2,000, depending on the specific monitoring configuration of the equipment affected. This lightning-strike monitoring well damage problem is especially pronounced in areas of high thunder storm concentration, such as Florida, Kansas, Texas, Missouri, Louisiana, etc.
Existing Designs
One solution to the lightning strike problem has been the introduction of black Delrin as a material from which to make hydrological pulleys. Unfortunately, black Delrin contains a high carbon content, which conducts electricity. Thus, this proposed solution does not completely insulate encoder disks 20, electronic sensors 22, nor encoders 24 from lightning strike damage.